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 Post subject: 405nm Laser Pointer
PostPosted: Sun Oct 04, 2009 12:08 am 
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There has been some discussion on the Gem-A mailing list regarding the new laser pointers available which emit a beam at 405nm.
At first there was a discussion with their use aiding in the determination of natural vs. synthetic blue spinel.
I found a 405nm laser pointer on eBay and bought it for $34.
Today I wandered around Lang Antiques testing everything I had time to shine my laser on.
Results:
All diamonds exhibited fluorescence from moderate to intense.
CZ is inert.
Some emeralds fluoresced red, some inert. Probably having to do with color caused by chromium vs. vanadium.
All rubies glowed like hot coals.
Blue sapphires seemed to glow a subtle blue, until I stumbled on this Retro Brooch with sapphires that glowed a screaming red. The sapphires were inert when viewed in a regular SW LW UV box.
Picture with laser pointer shining on one of the sapphires:
Image

What do you think is going on with this?


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PostPosted: Sun Oct 04, 2009 1:09 pm 
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Firstly, you know you should have a pair of safety glasses designed for that specific wavelength? Especially flashing it off all the odd-angle reflective surfaces provided by a gemstone. The other nice thing about the safety glasses is that they remove the excitation wavelength, so that the fluorescence is much easier to see.

The problem I have encountered with using lasers to study fluorescence is that fingerprint oil fluoresces reddish-orangey-yellow. I haven't personally tried 405 nm, but I've tried 532 nm, 514 nm, 488 nm, and 457 nm... and they all cause fingerprint oil to fluoresce.

Any gemstone fluorescing under laser light should be "screamingly bright" fluorescence. If it only fluoresces reddish or orangey at a normal brightness you'd expect with a UV lamp, it is likely the fingerprint oil.

There is a way to avoid this problem. Instead of using a 405 nm laser, use a cheap 400 nm "UV" LED flashlight like this one. The laser, which is very bright, is strong enough to cause fingerprint oil (and, for example, the paint on the wall) to fluoresce. But the flashlight isn't bright enough to cause fingerprint oil to fluoresce.

Rubies definitely fluoresce strongly on their own under 405 nm. If you can stand to look closely enough, you should be able to see the path through the ruby that the laser light is taking... including reflections off different surfaces.

This points out another way to separate between gem fluorescence and fingerprint oil fluorescence... since the fingerprint oil is only on the surface, there will not be a distinct fluorescence-colored path through the gem.

Sapphire fluorescence occurs randomly, not linked to body color. So if you have one sapphire that is exceptionally bright like a ruby, there isn't much in the way of diagnostic information.

The emeralds on the other hand... I'd think finger oil. The diamonds... I don't know, because I don't play with diamonds.


Last edited by Brian on Sun Oct 04, 2009 2:38 pm, edited 4 times in total.

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PostPosted: Sun Oct 04, 2009 1:24 pm 
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Okay, I'm going to ask the "dumb" question: How do you know what nm the UV light is if it isn't listed? :? The eBay listing doesn't say 400nm ... how do you know it's 400nm? If I want to buy one at a store, how do I know what nm it is???

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PostPosted: Sun Oct 04, 2009 1:41 pm 
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Because it costs less than ten bucks and because they don't tell you what kind of UV it is. If it was a 395nm, 390nm, or 385nm LED, then it would be displayed proudly in the title. But 400 nm LEDs are common and cheap, so they don't make a big deal out of their exact nature.


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PostPosted: Sun Oct 04, 2009 2:23 pm 
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GIA used to sell "contrast control glasses" with their UV light boxes. These were nothing more than yellow plastic safety glasses. These completely remove the blue light.
When exposed to strong blue light such as 405 laser light the tears on your eyes fluoresce(just like fingerprints) and this was the logic behind the glasses. Clear plastic would help too though I doubt it would block 405nm.

You should be careful with that laser because if you are shining it on faceted stones it is possible for you to get enough energy back to bother your eyes.
Maybe not highly likely but still worth precautions for. If you shined it at a big diamond it could send the whole beam back at you.

The 405 laser is a logical extension of the ideas reiterated in the article by Don Hoover and Bear Williams that appeared in the British Journal.
Like LEDs they don't put out a zillion lines nor continuum the way mercury and deuterium lights do.

So for example if you look through almost any UV filter at a white light you can see that it passes also some deep red. But if there is no deep red in your source because its an LED or Diode Laser then you have only the UV.
The filter is still necessary because LEDs have a pretty broad bandwidth.


Lasers have the advantage of being closer to monochromatic (but not truly if you look at their spectra it is a comb shape) and also of being coherent which is why it can be dangerous to look at them , even fairly safe low power ones. Don't look at laser light through a microscope or other optical instrument. That is VERY dangerous.

I had not noticed 405s at that price. (I must be slipping :lol: ) They are probably available because I think that is the laser used in the blu ray player. Good technology fallout.


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PostPosted: Sun Oct 04, 2009 2:32 pm 
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With regards to the 405nm lasers, exactly true... the blu ray uses the violet 405s and so they are produced in quantity to make 'em economical. In contrast, if you want a 478nm blue laser pointer, you still have to pony up over a hunnert. And if you want a yellow laser pointer, there is even less demand, so those cost even more.


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PostPosted: Sun Oct 04, 2009 3:26 pm 
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I've added a 405nm reaction chart to The Gemology Project:
http://www.gemologyproject.com/wiki/ind ... r_Pointers

Please correct me IMMEDIATELY if I am wrong, but shouldn't we be able to use the laser pointer in our old black UV cabinets with the protective "window" and be OK?

Can anyone supply a link to a source for proper protective goggles? I think it would be best if they were neutrally colored so one could see the color of the proper color of the reaction without being tempted to remove the goggles. :oops:


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PostPosted: Sun Oct 04, 2009 4:23 pm 
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and we do want them to be cool looking ones...

8)


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PostPosted: Sun Oct 04, 2009 5:59 pm 
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A Wratten 2E filter would be perfect and any Wratten number 2 would be pretty good as would be a 3. There are some other numbers that would be better than nothing like 86 series color correcting and 12 minus blue.
Have to make em into kreepy goggles your self.

Of course Blu Blockers would do to if they still sell em.
http://www.blublocker.com/products.asp?dept=3

"Kodak Wratten Filters" by Tiffen

http://www.leefiltersusa.com/camera/pro ... E14614A4F/

http://www.leefiltersusa.com/camera/pro ... E357A115F/


Last edited by G4Lab on Sun Oct 04, 2009 6:32 pm, edited 2 times in total.

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PostPosted: Sun Oct 04, 2009 6:23 pm 
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If the UV box has the yellow "contrast control glasses" that Gene mentioned, then that would be better than nothing.

Just for Tim... this link shows some stylish and expensive laser safety goggles like my students and I use. If you can get past the price tag and click on the "specifications" link, you can choose from the range of possibilities.

Alas, there is no such thing as neutral goggles, because they all work by subtracting a given color range from the incoming light. I have blue goggles for use with red lasers, yellow goggles for use with green, blue, and infrared lasers, and rose-colored goggles for use with infrared lasers. Nothing like spending the day looking at the world through my stylish rose-colored glasses. :D


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PostPosted: Sun Oct 04, 2009 9:37 pm 
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So, can I use the yellow glasses for shooting. Or the ones for night skiing? Or are those different? :?:

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PostPosted: Sun Oct 04, 2009 10:42 pm 
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Those are pretty close.


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PostPosted: Mon Oct 05, 2009 1:17 pm 
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If all the sapphires fluoresce in the same fashion, it would suggest to me that they are synthetic.


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PostPosted: Mon Oct 05, 2009 1:23 pm 
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Hi William.
All sapphires fluoresce in the same fashion.
95% of them are cut with the table perpendicular to the optic axis, exhibiting textbook uniaxial optic figures, all contain natural mineral inclusions.
The saphs are natural and pretty damn cool!


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 Post subject: Additional reactions to 405 nm lasers
PostPosted: Thu Nov 12, 2009 3:12 pm 
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Thought I'd post a few reactions I saw- many unexpected, at least to me.

All light (golden to peachy, Sri Lanka or Jeffry Mine, both) hessonites and golden grossulars glowed a nice pink/orange; "cinnamon" hess's did not. Merelani mints glowed like crazy; my tsavorites are out on the wife's hand and cannot be observed right now :) Pink grossulars from Mexico also fluoresce (also called raspberry, from Sierra de Las Cruces, Mexico).



Spess, "malaya" (both tanz and madagasgar), and chrome pyrope (from AZ) did not fluoresce. No andradites (demantoids or topazolites) reacted. Uvarovites , like andradites of all flavors, did not fluoresce (neither finnish nor russian specimens). Also, orange garnets did not fluoresce, regardless of alleged species or source. Nor did Mali garnets from green through brown or any rhodolites. Color change garnets fluoresced weakly if at all (regardless of source- Voi, Umba valley, Madagasgar- or color)

Most nice color spinels glowed quite brightly, too; natural blues generally less to no reaction. Synthetic blue spinels (at least some dark ones) did NOT fluoresce, but are red under chelsea; LIGHT blue synthetic spinel fluoresces brightly.

A lavender Umba sapphire glowed orange/pink, and a vietnamese ruby on matrix specimen did too, but not a couple other more purplish rubys, at least not brightly. All rubys en cabochon I found glowed nicely, and more brightly than did similarly colored spinels in a piece of pakistani wedding jewelry.

Many sapphires- even approaching ruby tones- did not fluoresce.

Ce-doped YAG glowed super bright. Alleged blue YAG (haven't tested) did not, but green YAG (rough) did. "reconstructed" ruby from ITC in Shelby, MI (also made that green YAG) did fluoresce strongly, as did a 1/2 boule of pink sapphire.

Kunzite fluoresced.

Many opaque Swat emeralds do not; some have weak and patchy fluorescence. Aqua did not fluoresce, pezzazoaite... not sure.

Benitoite did not, nor did sapphirine.

A canary diamond also fluoresced.

Just data. Some negatives probably actually have weak fluorescence; most samples were examined in a bright office.

What a cool toy. And it seems to reliably distinguish most spinels from similarly colored garnets, excepting the peachy grossular range of tones that a very few spinels may approach. So it will stay in my tool box. Besides, it is really way too dangerous to let the kids play with.

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